Many solutions have been tried for delivering digital data services to customers over cable networks. Historically, cable networks were designed for community antenna television (CATV) delivery supporting 6 MHz analog channels that were frequency-division multiplexed into a radio-frequency (RF) medium that was primarily coaxial cable or coax. To support higher throughput and advanced digital services, many of these cable TV networks migrated to a hybrid fiber-coax (HFC) architecture. With the development of HFC networks to support advanced services, such as digital television channels, the capability to provide bi-directional data services also evolved.
At present bi-directional data services are often available to customers using systems based upon the DOCSIS (Data-Over-Cable Service Interface Specifications) industry standards promulgated by Cable Television Laboratories or CableLabs. The DOCSIS standards comprise many documents that specify mechanisms and protocols for carrying digital data between a cable modem (CM), generally located at a customer premises, and a cable modem termination system (CMTS), commonly located within the headend of the service provider. Within distribution networks in the cable industry, data flowing from a service provider to a customer premises is commonly referred to as downstream traffic, while data flowing from a customer premises to a service provider is generally known as upstream traffic. Although DOCSIS is a bridged architecture that is capable of carrying other network protocols besides and/or in addition to the Internet Protocol (IP), it is primarily designed and used for Internet access using IP.
Furthermore, for many cable system operators (also known as multiple system operators or MSOs) the primary market for selling services such as cable TV, Internet access, and/or local phone services has been residential customers. Although DOCSIS cable modems could be used by business customers, DOCSIS was primarily designed to meet the Internet access needs of residential users. To make the deployment of DOCSIS systems economically feasible, the DOCSIS standards were designed to support a large number of price-sensitive residential, Intemet-access users on a single DOCSIS system. Though home users may desire extremely high speed Internet access, generally they are unwilling to pay significantly higher monthly fees. To handle this situation DOCSIS was designed to share the bandwidth among a large number of users. In general, DOCSIS systems are deployed on HFC networks supporting many CATV channels. In addition, the data bandwidth used for DOCSIS generally is shared among multiple users using a time-division multiple-access (TDMA) process.
In the downstream direction the DOCSIS CMTS transmits to a plurality of cable modems that may share at least one downstream frequency. In effect the CMTS dynamically or statistically time-division multiplexes downstream data for a plurality of cable modems. In general, based on destination addresses the cable modems receive this traffic and forward the proper information to user PCs or hosts. In the upstream direction the plurality of cable modems generally contend for access to transmit at a certain time on an upstream frequency. This contention for upstream slots of time has the potential of causing collisions between the upstream transmissions of multiple cable modems. To resolve these and many other problems resulting from multiple users sharing an upstream frequency channel to minimize costs for residential users, DOCSIS implements a media access control (MAC) algorithm. The DOCSIS layer 2 MAC protocol is defined in the DOCSIS radio frequency interface (RFI) specifications, versions 1.0, 1.1, and/or 2.0. DOCSIS RFI 2.0 actually introduces a code division multiple access (CDMA) physical layer that may be used instead of or in addition to the TDMA functionality described in DOCSIS RFI 1.0 and/or 1.1.
However, the design of DOCSIS to provide a large enough revenue stream by deploying systems shared by a large number of residential customers has some drawbacks. First, the DOCSIS MAC is generally asymmetric with respect to bandwidth, with cable modems contending for upstream transmission and with the CMTS making downstream forwarding decisions. Also, though DOCSIS supports multiple frequency channels, it does not have mechanisms to quickly and efficiently allocate additional frequency channels to users in a dynamic frequency-division multiple access (FDMA) manner. Furthermore, while the data rates of DOCSIS are a vast improvement over analog dial-up V.90 modems and Basic Rate Interface (BRI) ISDN (integrated services digital network) lines, the speeds of DOCSIS cable modems are not significantly better than other services which are targeted at business users.
Because businesses generally place high value on the daily use of networking technologies, these commercial customers often are willing to pay higher fees in exchange for faster data services than are available through DOCSIS. The data service needs of businesses might be met by using all-fiber optic networks with their large bandwidth potential. However, in many cases fiber optic lines are not readily available between business locations. Often new installations of fiber optic lines, though technically feasible, are cost prohibitive based on factors such as having to dig up the street to place the lines. Also, in many cases the devices used in optical transmission (including, but not limited to, fiber optic lines) are relatively newer than the devices used in electrical transmission (including, but not limited to coax cable transmission lines). (Both electrical and optical transmission systems may use constrained media such as, but not limited to, electrical conductors, waveguides, and/or fiber as well as unconstrained media in wireless and/or free-space transmission.) As a result, generally more development time has been invested in simplifying and reducing the costs of devices used in electrical communication systems, such as but not limited to coax CATV systems, than the development time that has been invested in devices used in optical communication systems. Thus, although fiber optics certainly has the capability of offering high data rates, these issues tend to drive up the costs of fiber optic communication systems.
Furthermore, in deploying networks to support primarily residential access, the transmission lines of the MSOs generally run past many businesses. Thus, a technical solution that functions over existing HFC networks of the MSOs, that provides higher data rates than DOCSIS, and that has the capability of working in the future over all fiber networks is a distinct improvement over the prior art and has the capability of meeting the needs of a previously untapped market segment.